Multiple time programmable (MTP) memory are a common type of non-volatile memory (NVM). Because the manufacturing of the MTP NVM is simple; and the production cost is relatively low, the MTP NVM have gained wide applications. For example, the MTP NVM are used in many apparatus, such as embedded systems, PCs and peripheral components, telecom exchanges, cellular phones and internet, etc.; and used to store information including voice and image data, etc.
A memory cell of a double-gate MTP NVM includes a substrate having a well region; a select gate and a floating gate formed in the well region; a source region and a bit line region formed in the well region in the substrate at the two sides of the select gate and the floating gate; and a lightly doped region formed in the well region in the substrate between the select gate and the floating gate. The source region, the bit line region and the lightly doped region have a same doping type. The doping type of the source region, the bit line region and the lightly doped region is opposite to that of the well region.
However, the performance of the memory cells of the existing MTP NVM is not stable. The disclosed device structures and methods are directed to solve the stability problem and other problems in the art.